Gorilla, Western Lowland

Gorilla gorilla

The gorilla is the largest of the great apes with a standing height of 4 to 5.8 feet and an armspread of 6 to 6.9 feet. Weight for females is 134 to 308 pounds and for males 297 to 605 pounds. The face, ears, hands, and feet are bare, and the chest of old males lacks hair. A pad of skin and connective tissue, which is relatively dense and fibrous in nature, is present on the crown. Mature males have a saddle of whitish hair which extends onto the thighs and earns them the name “silverback."

The population is estimated at 40,000, although it is declining due to habitat loss, as well as poaching.

Diet

While gorillas are primarily terrestrial, like other primates they are capable of climbing. Surface locomotion is quadrupedal, the soles of the feet and the middle phalanges of the fingers being placed on the ground. Gorillas are reluctant to cross even the shallowest of streams. Platform nests are built for sleeping. They are diurnal, with most activity taking place between 6 a.m. and 6 p.m. Although they are nearly entirely vegetarian, some will accept meat or take insects. Gorillas are social, living in groups. When two groups meet they may ignore each other, temporarily associate, or express hostility. Groups can range from 2 to 30 in number and, if a group has more than one mature male, one will be dominant. Vocalizations consist of roars, barks, growls, grunts, purrs, croaks, hoots, squeaks and screeches. Flat or slightly cupped hands are beat in rapid alteration on the chest, abdomen, hips, tree trunks, the ground, or anything that is handy. This drumming sounds the alarm when danger threatens.

There is no evidence of a breeding season, and females give birth once every 3½ to 4½ years unless the infant dies. The estrous cycle lasts 26 days, with estrus being 1 to 3 days. Physiologic sexual maturity is 8 years for females and 10 for males, although breeding does not usually occur until 10 in females and 15 in males. During a lifetime a female usually only gives birth to 2 or 3 surviving infants. Mortality during the first year of life is 42%, as opposed to 5% in adults. A single young is born, weighing about 4 pounds. The infant is completely dependent on the mother for food and protection.